Install Nav in Honda Odyssey EX?

Hi,

I just purchased a used 1999 Honday Odyssey EX. The van does not have
the optional GPS Navigation system from Honda.

I want to know if it is possible to install a GPS Nav system
after-the-fact. I recognize that this would change the layout of the
dash, so I'm not even sure if it's possible. The GPS Nav system for the
Odyssey also runs the heaing & AC controls, so there are fewer knobs on
the dashboard. I'm guessing I would have to go to an auto wrecking yard
for the plastic dashboard frame stuff.

Should it be possible, what am I looking for? I've seen used DVD Nav
systems for sale that are supposed to work with several different model
Honda's, but I don't know exactly which model would work with my
vehicle. Further, if I found a '99 model that would work with my
vehicle, would its maps be horribly out-of-date and unable to be
updated?

Thanks in advance!